SX-Amp and NX-Amp

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#1,350
Continuing where I left off with Ovation NX- no time during the summer.

During procedure 5 - Testing and setup, when I reach step 6 the current is to high and cant make adjustment with R6. R30 and R22 become real hot. The issue is same for both modules.. I had to replace R30 and R22 due to overheating and haven't looked at the amp until now..

Any suggestions?

I have checked all parts several times.. My eyesight isn't what it used to be. I'll continue to look it over with a magnifier..

In the meantime maybe Bonsai or someone has a good place for me to start looking..

thanks!
 
#1,351
Before power up R6 should be set for maximum resistance, 1K Ohm. This is a change in revision 2.08 of the NX amplifier document. The latest revision is 2.09, I believe. If you are not using the latest document, you need to update as there are various changes that are important.
 
#1,353
Thanks guys, for the prompt response.

I've always just opened Ovation NX doc from website each time I work on the amp. 2.09 is what I'm looking at..

From the start of testing I was aware R6=1k. I now checked again and it is 1kohm which is counterclockwise..

Hmm, Not sure.. No point powering up, same problem is going happen..
I'll keep looking..

?

Thanks!
 
#1,355
Bonsai said:
Joel, make sure you have the correct transistors in the Vbe multiplier and have not accidentally put the wrong gender ones in. I've done this before.
Click to expand...
" The collectors of the TIS transistors Q6 and Q7 are tied
together by the class AB bias control amplifier, configured around Q3, Q20, R6, R8,R20 and R21.This circuit simply multiplies (hence the commonly used name ‘Vbe multiplier’) the base emitter voltage of Q3"


I checked all devices around the circuit you suggested. looks good!

I examined my complete board and cross referenced to Circuit diagram, board overlay and the picture of the board with parts installed. Turns out I had installed 15 ohm resistors at R28 & R29, should be 120 ohm..

I had 100 ohm resistors on hand so added those for 115 ohms..
I'll try it now..

I looked at the boards on ebay, V1 vs V2.. V2 is now printed 120 for R28 and R29.
 
#1,356
You have to look back through the thread a ways now but I was one of the first here to build the Jim's Audio boards V1. I had a lot of issues of which Bonsai and I worked through. There were a few changes that had to be made to get the amp to perform properly. I believe those changes are what prompted V2. It might be worth your while to read through that process and Andrew explained things along the way. I believe Joe was part of that as well and offered some advice pertaining to the PSU/protection board as well.

Blessings, Terry
 
#1,357
R36 and R37 were changed from 15 Ohms to 150 Ohms at the same time when R28 and R29 were changed. See page 56 of the version 2.09 document for the update history.

When you tested the power board (pages 30 and 31 in document version 2.09) did all the voltages measure correctly?
 
#1,358
Yes, these resistors were changed following the issues Terry found. With the 15 Ohm resistors, if the Vbe's of the diamond level shifter transistors are higher than the front end buffer devices, you can end up with both or either one not turned on. The change to 150 ohms completely solves this problem.

115 ohms for testing is ok, but you should put 150 Ohms in - ie I would not leave it like that for normal operation.

Note: if you are LUCKY as I was with my proto and final builds, the front end can still work ok with the 15 Ohm resistors. However, this is pure luck. You must use 150'as described in the V2.09 doc.

Good luck with your build.
 
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#1,359
I installed 115 ohm for r28 and r29 - they were 15 ohm before.

My PS works properly, -52V/+52V

So I've connected V-, V+ and power Ground and zobel
Ammeter across V+ fuse holder
Fuse in V- fuse holder
R6=1kohm

R28 is smoking..

Is R3 adjustment important at this setup stage.
 
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